Star gerotors are positive-displacement fluid pumping devices having meshed inner and outer rotors. The inner and outer rotors are typically referred to as a star member and a ring member, respectively. Each rotor has a fixed center point that is eccentric with respect to the center point of the other rotor. The star member has n teeth, and is circumscribed by the ring member having (n+1) lobes. Rotation of one rotor drives the other, with a low relative speed maintained between the two rotors. The volume defined between the mating teeth/lobes of the engaged rotors creates a vacuum during gerotor rotation, and thus a resultant suction or intake stage for each revolution of the gerotor.
A steering control unit (SCU) of a hydrostatic power steering system is one type of fluid control device that commonly uses a star gerotor in its construction. An SCU may experience slip between its rotating gerotor members and a stationary member, e.g., an end cap which is secured adjacent to the gerotor. For example, when a steering cylinder controlled via a valve housing section of the SCU reaches the limit of its range of travel, a steering wheel controlled via the SCU may still rotate beyond this limit. Such additional rotation is often a result of internal fluid leakage between the star member and an adjacent surface of the stationary end cap.